This invention relates to apparatus for controlling RF signals. More particularly, it is concerned with apparatus for controlling the power supplied to a load by an RF signal generator.
In the past it has been difficult to provide precise control of the power supplied to a load, particularly a load of varying impedance, by an RF signal. Feedback control techniques have been employed to obtain approximate power control using an error signal derived as a function of the output voltage or the output current from the RF signal source. Error signals for feedback control have also been developed from the reflected and forward waves on a transmission line. This technique permits approximate power control over a limited dynamic range.
The foregoing methods provide only indirect approximations of the RF power delivered to the terminating load and only over a relatively narrow range of load impedance. In addition, the limited control function of these techniques can be effectively implemented over only a restricted power range and a restricted bandwidth.